Oats (Avena sativa) have unique characteristics which set them apart from other cereal grains. Oats contain a significantly higher protein concentration (15-20%) than other cereal grains (Peterson and Brinegar, (1986) in Oats: Chemistry and Technology, F. H. Webster, ed., Am. Assoc. of Cereal Chemists, Inc., St. Paul, Minn.). Oats also have one of the highest oil contents of the cereal grains.
Similar to other cereal grains, oat oil can be isolated from the oats by extraction with organic solvents. Oat oil has been noted for its variety and concentration of antioxidants (Youngs, (1986), ibid.; Hoseney, (1986) Principles of Cereal Science and Technology, F. H. Webster, ed., American Association of Cereal Chemists, Inc., St. Paul, Minn.); Hammond, (1983) in Lipids in Cereal Technology, P. J. Barnes, ed., Academic Press, New York). The peroxide value of a lipid provides an indication of the amount of rancidity-inducing peroxide radicals present in the lipid and is inversely correlated with product stability. The peroxide value is a titration which measures the levels of organic peroxides present in a fat and is a measure of the oxidative stability of the fat, and, thus, its antioxidant effectiveness.
Freshly-prepared oat oil has a peroxide value of zero, while oils from other cereal grains have higher peroxide values. When the peroxide value of an oil reaches about 20 or 25, the oil is usually contains detectable rancidity in its taste or odor. Two of the principle antioxidants found in oats are esters of caffeic and ferulic acid which exhibit some structural similarity to the synthetic antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). In addition, other antioxidants including tocopherols, tocotrienols, and o-aminophenol and its esters are also found in oats and several of these are probably present in the extracted oil.
As mentioned above, oil is generally recovered from cereal grains by extraction with organic solvents, typically hexanes or heptanes. The solvent is then eliminated by evaporation, typically distillation. The resulting crude vegetable oil contains numerous fine particles consisting predominantly of proteins (20-60%). The crude oil is then subjected to various refining steps including filtration to remove particulates, water washing to remove solids and gums, acid washing to remove phosphatides, alkali neutralization to remove free fatty acids, chilling ("winterization") to remove high-melting triglycerides, decolorizing ("bleaching") with activated bleaching earth or activated carbon, and deodorization by heating under high vacuum. Hydrogenation can also be performed to increase stability by increasing the chemical saturation state of the fatty acids in the oil.
A variety of oils have been used in dermatological formulations. For example, the use of both rice bran oil (U.S. Pat. No. 3,988,436 to Loo) and coffee bean oil (U.S. Pat. No. 4,793,990 to Grollier et al.) as sunscreen agents has been described. The Loo and Grollier et al. patents discuss the UV absorption properties of the oils. However, the patents do not indicate antioxidant action.
Nevertheless, it is established that vegetable seeds, cereal grains, and oils derived therefrom contain compounds that exhibit certain antioxidant activities. For example, the extracts from cereal grains treated with polar organic solvents, such as methanol, ethanol, and butanol, contain antioxidant activity (U.S. Pat. No. 2,975,066 to Baker et al.; U.S. Pat. No. 2,355,097 to Musher; Forsell et al., (1990) Chem. Abstracts, 113:189918w). When nonpolar organic solvents are used, the resulting extracts do not contain as high an antioxidant activity (U.S. Pat. No. 2,176,037 to Musher). Further, the prior art only teaches the use of highly purified oils for use as antioxidants (U.S. Pat. No. 2,355,097 to Musher; U.S. Pat. No. 4,211,801 to Oughton). There is no teaching in the prior art of the use of crude, largely unrefined oat oil as an antioxidant.
Antioxidants are important in skin care products since a major cause of photoaging is believed to be uncontrolled lipid peroxidation in the skin. This peroxidation is caused by the generation of free radicals when photons of ultraviolet light strike the skin. These radicals cause damage to vital skin components and also induce localized inflammatory responses.
Ultraviolet light or chemical initiators of oxidation have been shown to cause lipid peroxidation of methyl linoleate with free radical formation (Sugiyama et al., (1984) J. Dermatol., 5:455-459; Baker and Wilson, (1966) J. Lipid Res., 7:349-356; Baker and Wilson, (1966) J. Biol. Res., 7:341-348). The addition of antioxidants to this system has been shown to inhibit the peroxidation of methyl linoleate and result in a decrease in the formation of lipid peroxidation by-products such as malonyldialdehyde (MDA) (Niki et al., (1984) J. Biol. Chem., 7:4177-4182; Chedekel and Zeise, (1988) Lipids, 23:587-591).
Despite the variety of oils available for use in dermatological compositions and their many apparent functions, there remains a need for readily available, naturally-occurring, non-toxic oil compositions that are easily isolatable and are effective in multiple dermatological applications, such as in antioxidant, antiperoxidation, antiaging, and antiwrinkle applications.